1. Field of the Invention
The present invention relates to hydroxy-containing copolymers of dicyclopentadiene and maleic anhydride, useful for the sizing of paper.
2. Description of the Prior Art
U.S. Pat. No. 3,188,303 contains a description of products which are created during the transformation of .alpha.,.beta.-unsaturated di- and tricarboxylic acids, and maleic anhydride in particular, with dicyclopentadiene, at temperatures below 115.degree. C., in the presence of radical initiators in an inert solution. The temperature is limited to about 115.degree. C. in order to prevent a dedimerization of dicyclopentadiene into cyclopentadiene, with a subsequent Diels-Alder-reaction between cyclopentadiene and maleic anhydride. Aromatic or aliphatic hydrocarbons, respectively, such as, for instance, benzene, toluene, xylene, hexane, heptane or excess dicyclopentadiene may serve as solvent. Aside from these solvents, ethers such as dioxane or ketones may be used, but the reaction product must then first be precipitated by means of a hydrocarbon.
Compounds of the group of organic peroxides, hydroperoxides, oximes, nitriles, azo-aromatic and diazo-aromatic compounds may be used as radical initiators, as long as they have a sufficiently high speed of decomposition below the given reaction temperature, in order to start and maintain the reaction.
As the preferred radical initiators have been mentioned azobisisobutyronitrile, laurylperoxide, benzoylperoxide, 1-azocyclohexanecarbonitrile as well as t-butylperbenzoate.
The products resulting from the reaction are brittle powders which do not melt up to a temperature of 300.degree. C., and begin to decompose above this temperature. In this, they are clearly different from products created by a Diels-Alder-reaction between cyclopentadiene and maleic anhydride, and which melt in a temperature range between 30.degree. C. and clearly below 300.degree. C.
In addition, German Disclosure No. 2,727,510 describes the use of water-soluble ammonium salts of such copolymers from dicyclopentadiene and maleic anhydride as a material for the sizing of paper. Use of these synthetic paper sizings for surface treatment of paper permits their application without the addition of metallic salts. The copolymers listed there have the advantage over such other copolymers made from unsaturated carboxylic acids and ethylene-unsaturated compounds which are used for the sizing of paper, in that they may be used directly as copolymers or salts of copolymers, respectively, without having to be transformed into derivatives, such as semi-amides, imides, semi-esters, etc. The obtained values of efficiency are very good. The disadvantage of these copolymers mentioned in DE-OS No. 2,727,510, made of dicyclopentadiene and maleic anhydride lies in their anti-solubility in alkaline solutions (below 5%). They must, therefore be dissolved in aqueous ammonia solutions. After that, their possibilities for application become limited, wherever for reasons of production technology or physiology the use of ammonia is prohibited.